a survey of the polysaccharide reserves in geophytes ... · fructan (e.g. ornithoga/um pruinosurn)...
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50(//11 African Journal o( Botany 2001 6 7 371- 375 Ponied III South Afnca - All nghrs res€lYed
Copynghr ~ NISC Pry Ltd
SOUTH AFRICAN JOURNAL OF BOTANY ISSN 0254-6299
Short Communication
A survey of the polysaccharide reserves in geophytes native to the winterrainfall region of South Africa
B Orthen
Institut fOr Okologie der Pflanzen, Westfiilische Wilhelms-Universitiit, Hindenburgplatz 55,48143 Munster, Germany e ·mail: [email protected]
Received 11 January 2000, accepted in revised form 5 June 2000
Underground organs of 63 geophytic species, representing eight families of Monocotyledonae and five families of Dicotyledonae, native to the w inter-rainfall region of South Africa, were analysed for their polysaccharide storage components, With respect to type of polysaccharide accumulated in the storage organs the species tested can be divided into three groups: I) geophytes storing starch, II) geophytes storing fructan, III) geophytes storing both , fructan and starch, Most of the geophytes tested showed a capacity for storing large to massive amounts of polysaccharides. Starch andlor fructan contribute more than 40% to total dry mass of the underground storage organs, Within a family or a genus, species cannot naturally be placed in one group, e,g, members of the genus Omithogalum or Lachenalia
The winter-rainfall region of South Africa comprises one of the richest geophytic floras of the world (Cowling et al. 1999); the geophytic life-form can contribute up to 40% of the totat flora (Snijman and Perry 1987). According to Raunkiaer (1907) the characteristic feature of the geophyte life-form is being able to evade unfavourable environmental conditions in the form of underground storage organs. For the geophytes under investigation these unfavou rable environmental conditions are the high temperatures and drought during the summer months. The seasonal cycles of geophytes are synchronised with the climate in such a way that these plants are actively growing only when temperature and moisture regimes offer comparatively favourable conditions during winter and spring. Thereafter the aerial parts die-back and the plants remain as underground storage organs unti l the next growing season (Du Plessis and Duncan t 989).
Such a growth strategy must be based on a large supply of reselVe materials in the storage organs of the plants, Only with the help of these reselVes is the initiation of growth following seasonal dormancy possible. The possession of a storage organ also allows plants some independence from the periodicity of its habitat. Flowering, for example, can be achieved earl ier than in an annual which has to germinate
store either fructan or a combination of fructan and starch in the underground storage organs. However, all geophytes belonging to group III are members of the Monocotyledonae. In underground storage organs fructan was previously considered to be one alternative to starch: species rich in fructan do not accumulate more than traces of starch and vice versa. This survey demonstrates that this assumption can not be confirmed in the results for the underground storage organs of the South African geophytes, The majority of geophytes belonging to group III accumulated more than 20% of the total amount of polysaccharides as the minor component. In these geophytes fructan is accumulated in addition to and not as an alternative to starch ,
and pass through a juvenile phase with a bui ld-up of vegetative structure to support Ihe demand of flowering and subsequent seed maturation . Alternatively it can be completely separated from above ground vegetative development (hysteranlhous or proteranthous species) due to the availability of food reserves (Rees 1992).
There are few studies on the polysaccharide fraction of South African geophytes. Data on carbohydrate reselVes of geophytes nalive to the winter-rainfall reg ion are available for two species only. 80th species - one bulbous species in the Amaryllidaceae (Haemanthus pubescens) and one cormous species in the Iridaceae (Sparaxis grandiflora) - contain starch as the reserve polysaccharide in the underground storage organ (Ruiters et ai, 1993, Ruiters and McKenzie 1994), The bulbs of Nerine bowdenii, a geophyte native to the summer-rainfall region of South Africa, also store starch as the predominant polysaccharide (Theron and Jacobs 1996). Fructan, the reselVe polysaccharide of approximately 15% of the angiosperm flora (Hendry 1993), was not present (Haemanthus pubescens, Ruilers et al. 1993; Sparaxis grandiflora, Ruiters and McKenzie 1994) or detectable as traces only (Nerine bowdenii, Theron and Jacobs 1996),
The aim of th is survey was to determine the major polysaccharide reserves of the underground storage organs of
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various geophytes from different taxonomic families (Amaryllidaceae, Anthericaceae , Asphodelaceae , Colchicaceae, Eriospermaceae, Hyacinthaceae, lridaceae, Tecophilaceae , Asclepiadaceae . Asteraceae, Campanulaceae, Droseraceae, Oxalidaceae) native to the winter-rainfall region of South Africa.
The underground storage organs were collected in the field (South Africa, Kalkgat, 31°0S'S, 18°SS'E) or in the glasshouse (University of Munster, Germany) where plants were raised from seeds obtained from the National Botanical Garden, Kirstenbosch, Cape Town.
Sampling was carried out at the end of the growing season. After harvesting , storage organs were thoroughly cleaned. Fresh weight was determined immediately and the material was killed in a microwave for 3- 10 seconds. Samples were then dried at BO°C to constant mass , weighed, ground and extracted with water (10mg dry mass per ml a, dest.) for 1 hour. After centrifugation the supernatants were used for a modified fructan assay obtained from Megazyme (I reland) and the determination of water soluble starch (as hexose units after breakdown with amyloglucosidase). The insoluble residue was subjected to starch determination. After threefold extraction with 80% ethanol the starch was degraded by a-amylase (EC 3.2.1.1) and amyloglucosidase (EC 3.2.1.2) into its monomer glucose which was determined enzymatically according to Bergmeyer (1970).
The type of polysaccharide accumulated within the storage organs of the 63 species tested, representing eight families of Monocotyledonae and five families of Dicotyledonae, can be divided into three groups: I) geophytes storing starch, II) geophytes storing fructan and III) geophytes storing both, fructan and starch.
Group I
Twenty four species - Monocotyledonae as well as Dicotyledonae - stored starch as the only polysaccharide reserve in the underground organs (Table 1). Within this group four species (Androcymbium sp., Ferraria crispa, Fockea sp., Drosera cistiflora) stored starch in a range from 90-100g kg ' dry mass and can be regarded as low starch storing species . Twelve species accumulated between 20 and 40% dry mass as starch. Eight species showed the capacity to accumulate more than 40% dry mass as starch and can be regarded as high starch storers (Babiana cedarbergensis, Babiana nana, Babiana truncata, Freesia viridis, Lapeirousia pyramidalis, Moraea nana, Moraea serpentina, Cyanella hyacinthoides). Within one familiy (Inidaceae) there was a range in the storage of starch from high amounts (743g kg" dry mass Babiana truncata) to low amounts (99g kg" dry mass Ferraria crispa). The capacity to store starch is shown by geophytes with tubers (e.g. Drosera cistillora) , corms (e.g. Moraea serpentina) or bulbs (e.g. Oxalis f/ava) as underground storage organs. Starch is also used as a reserve polysaccharide by geophytes possessing a perennial storage organ (e.g. Fockea sp.) as well as by those which replace the storage organ annually (e.g. Moraea serpentina).
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Table 1: Geophytes storing starch (g kg' dry mass) as the only reserve polysaccharide in the underground organs (group I) . Samples were taken at the end of the growing season
Fami l}l: Species Starch Colchicaceae Androcymbium cillOlalum Sch tr.
and K. Krause 90 Iridaceae Babiana cedarbergensis GJ.l ewis 843
Babiana nana (Andr.) Spreng. 552 Babiana truncata GJ .Lewls 743 Babiana sp. 330 Ferraria crispa Burm. 99 Ferraria divaricata Sweet 204 Ferraria sp. 167 Freesia viridiS (AiL) Goldbl and Manning 711 Gladiolus sp. 184 Ixia sp. 301 Lapeirousia anceps (l. f.) Ker-Gawl . 349 Lapeirousla pyramidalis (l am.) Goldbl. 751 Moraea fugax (de la Roche) Jac. 129 Moraea nana Goldbl. and Manning 4t2 Moraea serpentma Baker 633 Romulea f/ava (lam.) De Vas 250 Romulea atrandra GJ. Lewis 198 Romulea setifolia N. E. Br. 312
Tecophilaeaceae Cyanefla hyacinthoides l . 620 Asclepiadaceae Fockea sp. 98 Droseraceae Drosera cistiflora l . 94 Oxalidaceae Oxalis f/ava L. 250
Oxalis sp. 191
Group /I
From the 63 geophytes surveyed 24 species accumulated fructan as the only polysaccharide in the storage organs (Table 2). These species belong to six families, four Monocotyledonae (Amaryllidaceae , Asphodeleaceae, Eriospermaceae, Hyacinthaceae) and two Dicotyledonae (Asteraceae, Campanulaceae) . Total Iructose polymers varied from 20Sg kg ' dry mass in Gethyl/is vil/osa to 729g kg , dry mass in Lachenalia mathewsii. Thirteen geophytes accumulated more than 40% dry mass as fructan and can be regarded as high fructan storing species. Among the species tested, fructan is found as the only polysacchanide reserve in perennial organs, bulbs (e.g. Urginia physodes) or stem tubers (e.g. Othonna hederilo/ia).
Group 11/
The underground storage organs of fifteen species out of the 63 geophytes tested were fructan and starch positive (Table 3), all these species belong to the Monocotyledonae. Except for Ch/orophytum undu/atum where the underground storage organ is a modified root these geophytes are characterised by the possession of bulbs. The total polysaccharide content varied between 176g kg ' dry mass (Ch/orophytum undu/atum) and 784g kg ' dry mass (Lachena/ia a/aides). Storage organs of 12 geophytes contained more than 40% dry mass as fructan and starch. In the bulbs of Brunsvigia sp., Crossyne flava, Massonia depressa and A/buca sp.
South African Journal of Botany 2001. 67 37-375
Table 2: Geophytes storing fructan (g kg 1 dry mass) as the only reserve polysaccharide in the underground organs (group II ). Samples were taken at the end of the growing season
Family Species Fructan AmarylJidaceae Gethyllis villosa (Thumb.) Thumb. 205
GethylJis sp. 267 Asphodeleaceae Bulbine mesembryanthemOldes Haw. 367
Bu/bine torta N. E. Br 520 Bu/bine sediflo/fa Schhltr. ex. V. Poelln. 632 Bu/bine sp. 460 Traeheandra falcala (U.) Kunth 312 Tracheandra kaooriea Oberm. 206 Traeheandra tortillis (Bak.) Oberm. 484
Eriospermaceae Eriospermum sp. I 244 Eriospermum sp. II 295
Hyacinthaceae Albuca spiralis L.f. 583 A/buea sp. 478 Laehenalia trichophylla Bak. 560 Laehenalia mathewsii W.F. Barker 729 Lachena/ia vio/aeeae Jacq. 287
Ornithogalum Omithoga/um mUIti/oHum Jacq. 378 Ornithoga/um cf. nanodes F.M. Leight 682 Omithogafum unifolium Retz. 614 Rhadamanlhus platyphyflus B. Nord. 310 Urginia physodes (Jacq.) Baker 419
Asleraceae Othonna hederifolia B. Nord. 630 Othonna eaelioides L.f 378
Campanu!aceae Cyphia oligotrieha Schllr. 484
starch content was higher than fructan content, whereas in the other species fructan content was higher. The fructan~ slarch ratio demonstrates that it is possible to distinguish between organs where either starch (e.g. Brunsvigia sp.) or fructan (e.g. Ornithoga/um pruinosurn) is the predominant polysaccharide and those where both carbohydrates are stored to similar amounts (e .g. Lachena/ia minima).
Most 01 the geophytes tested, showed a capacity to store large to massive amounts of polysaccharides: Where starch and/or fructan contribute more than 40% of total dry mass of the underground storage organs.
Starch, the most common storage carbohydrate in vascu~
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lar plants, was detected in the underground storage organs of 38 out 01 the 63 geophytes sUNeyed (Table 1, Table 3). The amount 01 starch accumulated in the bulbs, corms and tubers differs considerably (from 90-843g kg ' dry mass, Table 1). The maximum value 01 84% dry mass in the corms of Babiana cedarbergensis was in the same range as the starch content of plants commercially used as starch sources (e.g. potato tubers: 86% dry mass, Paul and Southgate 1978).
Fructan, the reserve carbohydrate of approximately 15% 01 the angiosperm flora (Hendry 1993), was stored by 38 species, representing 6 monocotyledonae and two dicotyledonae families (Table 2, Table 3). Within this group of Iructan storing species maximum values of up to 73% dry mass have been obseNed (Table 2). Again, these amounts are similar to those detected in commercially used species (Cichorium inlybus, Helianlhus luberosus, Incoll and Bonnett 1996).
It has been suggested that the occurrence of fructan may be related to phylogenetic relationship (Pollard and Amuti 1981, Smouter and Simpson 1989, Tertuliano and Figueiredo-Ribeiro 1993). Pollard (1982) reports a sUNey 01 Monocotyledons. It was demonstrated that Iructan is restricted; within a given family fructan occurred consjstent~
Iy in every representative plant. Within the monocotyledonae under investigation all species belonging to the Amaryllidaceae, Anthenicaceae, Asphodelaceae, Eriospermaceae and Hyacinthaceae were fructan positive (Table 2) . Interestingly, all species tested belonging to the Iridaceae (Babiana, Ferrar;a, Lapeirousia, Moraea, Romubea, Ixia) - a family known for Iructan storing species (e.g. Meier and Reid 1982, Hendry and Wallace 1993) - were Iructan negative and stored starch (Table 1).
Except for the Asteraceae Olhonna hederifolia, Olhonna cacalioides and the Campanulaceae Cyphia oligolricha, which are Iructan storers (Table 2) , the other Dicotyledonae species tested accumulated starch as polysaccharide reseNes (Table 1).
In 15 species starch as well as fructan was present in bulbs and root tubers (e.g. Lachenalia a/oides, Ch/orophylum undu/alum, Table 3) . Except for the bulbs of
Table 3: Geophytes storing fructan as weI! as starch (g kg 1 dry mass) in the underground organs (group III) and the fruclan to starch ratio. Samples were taken at the end of the growing season
Family Species Fructan Starch F.lSt. AmarylUdaceae Brunsvlgia radula (Jacq.) Ail. 128 542 0.2
Brunsvigia sp. 101 657 0.2 Crossyne flava (Snijman) D. and U. MII~Doblies 189 336 0.6
Anthericaceae Chlorophytum undulatum (Jacq.) Oberm. 125 51 2.5 Hyacinthaceae Laehenalia aloldes (l.t.) Asch. and Graebner 592 192 3.1
Laehenalia eontaminata Ail. 515 100 5.2 Laehenafia minima W.F Barker 408 304 1.3 Laehenafia undufata Masson ex Bak. 260 147 1.8 Laehena/ia zebrina W.F Barker 357 99 3.6 Massonia echinata L.f 250 183 1.4 Massonia depressa Houtt. 306 450 0.7 Ornithogalum dilueulum Oberm. 250 150 1.7 Ornithogalum ova tum Thunb. 397 96 4.1 Ornithogalum pruinosum Leighton 300 50 6.0 Albuea sp. 203 251 0.8
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Brunsvigia sp., Crossyne flava, Massonia depressa and Albuca sp. fructan content was higher than starch content. The fruetan/starch ratio differed considerably: in some species starch content was much lower than truetan content (Lachenalia contaminata, Ornithogalum pruinosum) , in others the accumulation of starch nearly equaled that of truetan (Lachenalia minima, Massonia echinata) .
In leaves the co-occurrence of starch and fructan is a wellknown phenomenon (e.g. Chatlerton et al. 1989, Housley and Pollock 1993, Kelly and van Staden 1994, Wang and Tillberg 1997). As a reserve carbohydrate in underground storage organs fruetan was considered as one alternative to starch - species rich in fructan do not accumulate more than traces of starch (Pale and Dixon 1982, Brocklebank and Hendry 1989, Tertuliano and Figueiredo-Ribeiro 1993). This survey demonstrates that this assumption cannot be confirmed in the results for the underground storage organs of Ihe South African geophyles. The majorily of geophyles belonging to group III accumulated more than 20% of the total amount of polysaccharides as the minor component. In these geophytes fructan was accumulated in addilion to and not as an alternative to starch.
The queslion of whether the slorage of fructan instead of starch is of any benefit fo r the planl is still a matter of debale. Atlempts have been made to establ ish a function of fructan beyond its role as a reserve carbohydrate , two additional functions have received much attention in the literature in its role as an osmoregulator and as a solute in stress - cold or drought - adaptation (e.g. Pontis 1989, Pollock and Crains 1991 , Hendry 1993; Pilon-Smits et al. 1999).
A survey on Ihe reserve carbohydrales of 20 species of the Sheffield tlora (UK) led Brocklebank and Hendry (1989) to the conclusion that fructan storage is associated with relatively restricled phenologies, whereas Ihe slorage of starch is associaled with the broadesl variation in phenological patterns. The phenologies related to the storage of fructan were early and low lemperalure growth (Brocklebank and Hendry, 1989). Phenological data for the South African geophytes are limited; a study by Van Rooyen et al. (1979) conducted on plants in the Goegap Nature Reserve (17"57'E, 29"34'S) includes 7 geophytes which are part of this survey as well. Neilher the species storing only fruclan (Bu/bine sedilolia, Trachenadra fa/cata) nor the species storing both fructan and starch (Massonia depressa, Ornithogalum pruinosum) showed significant differences in phenology when compared with the starch storing species (Babiana truncata, Cyanella hyacinthoides). Personal observations of the liming of regrowth following dormancy in the natural habilat as well as in the glasshouse revealed no significant differences between starch and/or fructan storing species.
Another aspeci with respect to phenology is Ihat fructan remobilisation is associated with rapid inflorescence development (Solhaug and Aares 1994) and rapid petal expansion (Bieleski 1993). The utilisation of fructan for rapid reproduction might be an advantage especially for hysteranlhous and proteranthous geophytes. In bOlh these groups flowering is completely separated from above ground vegelative development and occurs during the dry period.
The occurrence of bolh fructan and starch as reserve polysaccharides in subterranean organs has received little atten-
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tion. Histological studies on HeNanthus tuberosus showed that low amounts of starch are detectable in the tuber during tuber development, fructan synthesis and the beginning of sprouling, but not during dormancy (Ernst 1991). A comparable result was obtained for onion bulbs (Ernst and Butler 1994). Fructan, Ihe principle carbohydrate reserve is found Ih roughout the bulb (Darbyshire and Henry 1978), whereas Ihe occurrence of slarch is restricted to Ihe siems (= basal plate). Starch can be detected in its primary thickening meristem du ring sprouting but not during dormancy (Ernst and Bufler 1994).
These results allow for speculalion thai these two reserve carbohydrates fulfil different roles during specific phenological phases (e.g. resprout ing , reproduction, dormancy). For the geophytes with a similar fructan and starch content in the storage organs (Table 3) in particular, a differenlial use of fructans and starch seems possible and would ensure that there is always carbon available should adverse conditions prevai l.
Acknowledgements - Thanks are due 10 Ihe owner (Prof. Dr Kuhlmann) and the scientific administrator (prof Dr von Willert) of Kalkgat as well as to Cape Nature Conservation for gettmg the permission to remove the geophytes. Thanks go to the staff of the Compton Herbarium for the help with the plant identification. The technical assistance of H. Schwltle is gratefully acknowledged.
References
Bergmeyef HU (1970) Methoden den enzymalischen Analyse . Vol. 2. Verlag Chemie, Weinheim
Bieleski R.l (1993) Fructan hydrolYSIS drives petal expansion in the ephemeral daylily flower. Plant Physiology 103: 213-219
Brocklebank KJ , Hendry GAF (1 989) Characteristics of plants wh ich store different types of reserve carbohydrates. New Phytolologist 112: 255-260
Chatterton NJ , Harrison PA, Bennett JH , Asay KH (1989) Carbohydrate partitioning in 185 accessions of Gramineae grown under warm and cool temperatures. Journal of Plan t Physiology 134: t69-179
Cowling R, EslerKJ, Runde! PW (1999) Namaqualand, SoulhAfrica - an overview of a unique winter-rainfall desert ecosystem. Plant Ecology 142: 3-2t
Darbyshire B, Henry AJ (1978) The distribution of fructans in onions. New Phytologist 61 : 29-34
Ou Plessis N , Duncan 0 (19a9) Bulbous plants of Southern Africa. A guide to their cultivation and propagation. Tafelberg Publ ishers LTD, Cape Town
ErnSI M (1991) Histochemische Untersuchungen auf Inulin, Starke und Kallose bel Hel ianthus tuberosus l. (Toplnambur) . Angewandte Botanik 65: 319--330
Ernst M. Bufler G (1994) Stems of Allium cepa L. contain starch. New Phytol agist 128: 403-406
Hendry GAF (1993) Evolutionary origins and natural functions of fruclans - a climatological. biogeographic and mechanistic appraisal. New Phytologist 123: 3-14
Hendry GAF, Wallace RK (1993) The origin, distribution. and evolutionary significance of ffuctans. In: Suzuki M and Chatterton NJ (eds.) Science and technology of fructans . CRC Press, Boca Ralon, pp 119-139
Housley TL, Pollock CJ (1993) The metabolism of fructan in plants. In: Suzuki M and Chatterton NJ (eds.): Science and technology of fructans. CRC Press. Boca Raton. pp 191-225
Incoll LD, Bonnell GO (1996) Fructans in the Compositae a short
South Afncan Journal of Botany 2001. 67 37-375
review. In: Ca llgari PDS and Hind DJN (eds) Composltae: BIology and utilisation. Proceedings of the international Composltae conference , Kew, 1994. Vol. 2 pp 401-413, Roya l Botanic Gardens, Kew
Incoll LD, Bonnett GD, Gott B (1989) Fructans In the underground storage organs of some Australian plants used for food by aborigines. Journal of Plant Physiology 134: 196- 202
Kelly KM, Van Sladen J (1994) Carbohydrate production in guayule South African Journal of Botany 60: 193-202
Meier H, Reid JSG (1982) ReseIV8 polysaccharides other than starch in higher plan ts. In: Loewus FA and Tanner W (eds) Plant Carbohydrates I. Intracellular Carbohydrates. Encyclopedia of Plant Physiology Vol. 13A. Springer Verlag , Heidelberg
Pate JS, Dixon KW (1982) Tuberous, cormus and bulbous plants. University of Western Australia Press, Nedlands
Paul AA , Southgate DAT (1978) McCance and Widdowson's The Composition of food. 4th ed. HMSQ, London
Pilon-Smits EAH , Terry N, Sears T, Van Dun K (1999) Enhanced drought resistance in fructan-producing sugar beet. Plant Physiology and Biochemistry 37: 313-317
Pollard CJ (1982) Fructose oJigosaccharides in monocotyledons: possible delimita tion of the order Uliales. Biochemical Systematics and Ecology 10: 245--249
Pollard CJ, Amutl KS (1981) Fructose oligosacchandes: possible markers 01 phylogenetic relationships among dictoyledonous plant famities. Biochemical Systematics and Ecology 9: 69- 78
Pollard CJ , Crains AJ (1991 ) Fructan metabolism in grasses and cereals. Annual Review of Plant Physiology 42: 77-101
Pontis HG (1989) Fruclans and cold stress. Journal of Plant Physiology 134: 148-150
Raunklaer C (1907) Platerigets Ilvslormer og deres betydning lor geogralien. Nordlsk Veri. , Copenhagen
Rees AR (1992) Ornamental bulbs, corms and tubers. CAB International. Wallingford
RUlters C, McKenZie B (1994) Seasonal allocation and efficiency pa tterns of biomass and resources in the perennial geophyte
Edited by GJ Bredenkamp
375
Sparax;s grandiflora subspecies fimbria ta (Iridaceae) in lowland coastal 'ynbos, South Afrika. Annals of Botany 74: 633-646
Auiters C, McKenzie B, Aalbers J, Railt LM (1993) Seasonal allocation of biomass and resources in the geophyt ic species Haemanthus pubescens subspecies pubescens in lowland coastal fynbos, South Afrika . South African Journal of Botany 59: 251-258
Snijman D, Perry P (1987) A flonistic analysis of the Nieuwoudtville Wild Flower Reserve, north-western Cape. South African Journal of B01any 53: 445- 454
Smouter H, Simpson RJ (1989) Occurrence 01 fructans in the Gramineae (Poaceae). New Phytologist 111 : 359- 368
Solhaug KA, Aares E (1994) Remobilisation of fructans in Phippsia a/gida during rapid inflorescence development. PhysioJogia Plantarum 91: 219--225
Tertuliano MF, Figueiredo-Ribeiro RCL (1993) Distribution 01 fructose polymers in herbaceous species of Asteraceae from cerra· do. New Phyto[ogist 123: 741- 749
Theron KI , Jacobs 0 (1996) Changes In carbohydrate composition of different bulb components of Nerine bowdenii W_ Watson (Amaryll idaceae). Journal of the American Socie ty lor Horticultura l Science 121 : 343-346
Van Rooyen MW, Theron OK, Grobbelaar N (1979) Phenology of the vegetation in the Hester Malan Natu re ReselVe in the Namaqualand Broken Veld: 1, General observations. Journal of South African Botany 45: 279- 293
Wang C, Tillberg JE (1997) Effects of short- term phosphorus deficiency on carbohydrate storage in sink and source leaves of barley (Hordeum vulgare) . New Phytologist 136: 131-135